1. Field of the Invention
This invention relates generally to fiberscopes, and more particularly to a super-thin fiberscope which can be advantageously used, primarily but not exclusively, for medical and diagnostic purposes.
2. Description of the Prior Art
Fiberscopes themselves are not new. They have been popularly used in the medical field since the mid-1950's as well as in the industrial field since the mid-1960's.
Fiberscopes for use in the medical and diagnostic field are required to be super-thin and appropriately flexible to provide easy access to various targets within the human body. In addition, the fiberscope must also have a certain degree of rigidity to enable insertion into the human body by pushing. Further, despite the extremely small diameter, the fiberscope must ensure a clear image of the target for correct inspection.
Various attempts have been made to provide a super-thin fiberscope which meets all of the above requirements.
U.S. Pat. No. 4,593,973 to Yoshida et al discloses a super-thin fiberscope which comprises an image guide integrally contained in a transparent material body. The transparent body serves as a light guide and is formed with a through-bore for injection of a physiological saline solution. This transparent body is made of a resin, such as polymethyl methacrylate, polystyrene or polycarbonate, which has a high light transmittance.
The fiberscope of the above patent is disadvantageous in various respects.
Firstly, the light guide provided by the transparent resin body is far lower (about 1/10) in light transmittance than a conventional light guide provided by multi-component glass fibers. Therefore, in order to provide enough light for illuminating a target, the transparent resin body, hence the fiberscope as a whole, must be made relatively small in length when made extremely small in diameter. In fact, the fiberscope of this patent can have a diameter of not more than 0.7 mm only when used for dental application where a relatively short fiberscope is acceptable.
Secondly, the transparent resin body must be formed internally and externally with a cladding and possibly further with a fluorinated resin coating to eliminate light leakage and surface flaws, consequently increasing production cost.
In the third place, the transparent resin body, which is an integral body serving as a light guide, lacks flexibility and yet fails to provide a mechanical strength required for insertion into the human body.
The above U.S. patent further discloses as "Prior Art" a fiberscope which comprises a heat-shrinkable tubular casing accommodating an image guide, a plurality of light guide fibers, and a brine injection tube. However, the heat-shrinkable casing lacks mechanical strength, failing to realize a diameter of not more than 1 mm.